The present invention relates to a shock absorber with a leveling function mounted between the body and an unspring member of an automobile.
In general, the shock absorber is provided with a cylinder, and a piston rod, one end of which is mounted on a piston which slidably moves within the cylinder, and movably inserted into the cylinder, one out of the cylinder and the piston rod being connected to the unspring member, the other being connected to the body so as to obtain the damping force with respect to the vibrations of the unspring member.
On the other hand, there has been proposed a configuration in which a leveling cylinder is interposed between the shock absorber and the body or the unspring member, so as to perform leveling so that when the level is lowered, pressure fluid is supplied to the cylinder from a pressure source to raise the level. In this case, since a pump driven by the engine is used as a pressure source, the burden of the engine is heavy and the efficiency of fuel cost becomes worsened.
There has been further proposed a configuration in which a pressure medium which is changed into gas or liquid depending on the temperature is sealed into the leveling cylinder, a supply of current to a heater is controlled by means of a switch responsive to variation of the level, and the pressure medium is heated or cooled to thereby enable raising or lowering of the level. According to this proposal, the pump is not used, the burden of the engine is small, and the efficiency of fuel cost is good.
However, in the shock absorber with a leveling function as described above, since the electrothermal part of the heater is in direct contact with the pressure medium, an electrothermal area of the electrothermal part with respect to the pressure medium is so small that the pressure medium is heated in part intensively to generate bubbles around the electrothermal part, and a vapor film is formed by the bubbles to generate the burn-out phenomenon, as a result of which the heat conductivity with respect to the whole pressure medium lowers rapidly. As a consequence, there were problems such that the leveling control fails to be carried out with high accuracy, and in addition, the heater becomes deteriorated, and very offensive gases adversely affecting on seals or the like become generated.
The present invention has been accomplished paying attention to the conventional problems as noted above. It is an object of the invention to provide a shock absorber with a leveling function capable of, without placing an electrothermal part of a heater in direct contact with a pressure medium, transmitting heat of the electrothermal part to the medium sufficiently and effectively.
For achieving the aforementioned object, a shock absorber with a leveling function according to the present invention comprises a tubular case one end of which is connected to a piston rod airtightly and the other end thereof comes in contact with the outer circumference of a cylinder slidably, a holder for closing an open end on the piston rod connecting side of the case, a pressure chamber formed between the holder, the cylinder, the piston rod and the case to accommodate a pressure medium, and a heater plug in which an electrothermal part is fitted into a mounting hole formed in the thick-wall of the holder, wherein the electrothermal part is heat-generated to heat and vaporize the pressure medium in contact with the holder to raise pressure within the pressure chamber thus enabling leveling due to the relative displacement of the cylinder and the piston rod.
In this case, the electrothermal part is fitted into a mounting hole through a heat conductivity collar, and the heat conductivity collar is molded of copper, aluminum or other materials of good thermal conductivity.